Attending the city’s annual event can feel like entering a time capsule from a previous era. In the broad accent of old Boston, union leaders denounce corporate greed, passionately lobby for workers’ rights, and embrace politicians who promote their cause.

Senators Elizabeth Warren and Ed Markey, who both spoke at the breakfast, were each helped on election day by support from labor. This election cycle, it’s all about Walsh, the candidate who resigned as head of the Boston Building Trades to run for mayor and promises to wear his record “of fighting for working people as a badge of honor.”

“Walsh for Mayor” signs dominated the landscape at the Park Plaza Hotel, where the breakfast was held. As they passed out scrambled eggs, servers wore buttons declaring their support for Walsh. “Welcome to Ross country,” quipped City Councilor Michael Ross, one of several mayoral candidates who braved what was essentially a Walsh campaign rally.

For much of this crowd, winning means electing Walsh. Which raises some questions for him. What will he owe labor for victory, if it comes? As mayor, could he say no to union supporters once he is sitting across from them at the negotiating table?

In his breakfast speech, Walsh went out of his way to address the elephant in that ballroom packed with union backers: “Certain people,” he said, “are going to claim that labor unions are just another bunch of people looking out for number one. That couldn’t be more wrong. But just in case there’s anyone out there following this race who might wonder, let me state in the most direct and certain terms possible: I can and I will represent all the people of this city to the utmost of my ability, with fear or favor for none and with fairness for all.”

After the event, Walsh said that he could “absolutely” stand up when necessary to union supporters. As mayor, he said, “the voters and the taxpayers are the first priority for me. . . I’m not going to be the person giving the city away.”

Asked for examples of when he pushed back against the union agenda, Walsh offered these: He’s a founding board member of a charter school, which unions generally oppose, he said; as a legislator, he voted to take away some collective bargaining rights for teachers. He also opposed public funding of political campaigns, which the AFL-CIO once backed in Massachusetts via a “Clean Elections” ballot question.

That’s not the strongest case for his contention that he is willing to rebuff public employees on contentious collective bargaining issues. However, Walsh supporters argue that labor will trust him when he tells them the city has gone as far as it can, because he’s a union brother.

In a municipal election, where Boston’s building trade unions are among the most politically active, labor gives Walsh a crack at one of the two top spots in the Sept. 24 preliminary. Union organizers are his grass roots, supplying the network that will get Walsh voters to the polls. That, at least, is the theory. Labor has also been generous to him when it comes to campaign donations, helping him assemble a war chest that he can use for advertising in the crucial final stretch.

It’s Walsh’s best shot to the final. But if it delivers enough votes to put him there, union support can quickly turn into a disadvantage. To his rival’s delight, he will be labor’s candidate.

Despite Walsh’s protestations, the city’s public unions often do look like they are “out there for number one.’’ If he makes it to the final, Walsh will have to do more than say the perception is wrong. He will have to convince voters that looking out for number one will never prevail as reality for labor under a Walsh administration — no matter how strong his union backing.

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